<h2>DESCRIPTION</h2>

<em>r.ros</em> is part of the wildfire simulation toolset. Preparational
steps for the fire simulation are the calculation of the rate of spread (ROS)
with <em>r.ros</em>, and the creating of spread map with <em>r.spread</em>.
Eventually, the fire path(s) based on starting point(s) are calculated
with <em>r.spreadpath</em>.
<p>

<em>r.ros</em> is used for fire (wildfire) modeling. The input is fuel model
and moisture and the outputs are rate of spread (ROS) values.
The module generates the base ROS value, maximum ROS value,
direction of the maximum ROS, and optionally the maximum potential spotting distance
of wildfire for each raster cell in the current geographic region.
These three or four raster map layers
serve as inputs for the <em><a href="r.spread.html">r.spread</a></em> module
which is the next step in fire simulation.

<p>
The <em>r.ros</em> module and two related modules
<em><a href="r.spread.html">r.spread</a></em>,
and <em><a href="r.spreadpath.html">r.spreadpath</a></em> can be used
not only for wildfire modeling but also generally
to simulate other events where spread of something is involved and
elliptical spread is appropriate.

<p>
The calculation of the two ROS values for each raster cell is based on the
Fortran code by Pat Andrews (1983) of the Northern Forest Fire Laboratory,
USDA Forest Service. The direction of the maximum ROS results from the
vector addition of the forward ROS in wind direction and that in upslope
direction. The spotting distance, if required, will be calculated by a
separate function, spot_dist(), which is based on Lathrop and Xu (in preparation),
Chase (1984) and Rothermel (1991).  More information
on <em>r.ros</em> and <em><a href="r.spread.html">r.spread</a></em> can be found in Xu (1994).

<p>
The <b>output</b> parameter is a basename (prefix) for all generated
raster maps and each map gets a unique suffix:

<ul>
  <li><tt>.base</tt> for the base (perpendicular) ROS (cm/minute)
  <li><tt>.max</tt> for the maximum (forward) ROS (cm/minute),
  <li><tt>.maxdir</tt> for the direction of the maximum
    ROS, clockwise from north (degree), and optionally
  <li><tt>.spotdist</tt> for the maximum potential
    spotting distance (meters).
</ul>

<p>
So, if the output parameter is <tt>blackforest_ros</tt>, <em>r.ros</em> creates
<tt>blackforest_ros.base</tt>, <tt>blackforest_ros.max</tt>,
<tt>blackforest_ros.maxdir</tt>,
and (optionally) <tt>blackforest_ros.spotdist</tt> raster maps.

<p>If only one or two of the options <b>moisture_1h</b>, <b>moisture_10h</b>,
and <b>moisture_100h</b> are given, the module will assign
values to the missing option using the formula:

<div class="code"><pre>
moisture_100h = moisture_10h + 1 = moisture_1h + 2
</pre></div>

However, at least one of them should be given.

<p>
Options <b>velocity</b>
and <b>direction</b> must be both given or both omitted.
If none is given, the module will assume a no-wind
condition.

<p>
Options <b>slope</b> and <b>aspect</b> must be also given together.
If none is given, the module will assume a
topographically flat condition. Option
<b>elevation</b> must be given if <b>-s</b> (spotting) flag is used.

<h2>EXAMPLES</h2>
Assume we have inputs, the following generates ROSes and spotting distances:

<div class="code"><pre>
r.ros -s model=fire_model moisture_1h=1hour_moisture moisture_live=live_moisture \
    velocity=wind_speed direction=wind_direction \
    slope=slope aspect=aspect elevation=elevation output=ros
</pre></div>

<h2>NOTES</h2>

<ol>
  <li><em>r.ros</em> is supposed to be run before running
    <em><a href="r.spread.html">r.spread</a></em> module.
    The combination of these two modules forms
    a simulation of the spread of wildfires.
  <li>The user should be sure that the inputs to
    <em>r.ros</em> are in proper units.
  <li>The output units for the base and maximum ROSes are in cm/minute
    rather than ft/minute, which is due to that a possible zero ft/minute base
    ROS value and a positive integer ft/minute maximum ROS would result in
    calculation failure in the
    <em><a href="r.spread.html">r.spread</a></em> module.
    <!-- This is caused by usage of CELL instead of FCELL/DCELL. ? -->
    As far as the user just use <em>r.ros</em> together with
    <em><a href="r.spread.html">r.spread</a></em>, there is no need to
    concern about these output units.
</ol>

<h2>REFERENCES</h2>

<ul>
  <li><b>Albini,</b> F. A., 1976, Computer-based models of wildland fire behavior:
    a user's manual, USDA Forest Service, Intermountain Forest and Range Experiment
    Station, Ogden, Utah.</li>
  <li><b>Andrews</b>, P. L., 1986, BEHAVE: fire behavior prediction and fuel
    modeling system -- BURN subsystem, Part 1, USDA Forest Service, Intermountain
    Research Station, Gen. Tech. Rep. INT-194, Ogden, Utah.</li>
  <li><b>Chase</b>, Carolyn, H., 1984, Spotting distance from wind-driven
    surface fires -- extensions of equations for pocket calculators, US Forest
    Service, Res. Note INT-346, Ogden, Utah.</li>
  <li><b>Lathrop</b>, Richard G. and Jianping Xu, A geographic information
    system-based approach for calculating spotting distance. (in preparation)</li>
  <li><b>Rothermel</b>, R. E., 1972, A mathematical model for predicting
    fire spread in wildland fuels, USDA Forest Service, Intermountain Forest
    and Range Experiment Station, Res. Pap. INT-115, Ogden, Utah.</li>
  <li><b>Rothermel</b>, Richard, 1991, Predicting behavior and size of crown
    fires in the northern Rocky Mountains, US Forest Service, Res. Paper INT-438,
    Ogden, Utah.</li>
  <li><b>Xu</b>, Jianping, 1994, Simulating the spread of wildfires using
    a geographic information system and remote sensing, Ph. D. Dissertation,
    Rutgers University, New Brunswick, Jersey
    (<a href="https://dl.acm.org/citation.cfm?id=921466">ref</a>).</li>
</ul>

<h2>SEE ALSO</h2>

<em>
<a href="g.region.html">g.region</a>,
<a href="r.slope.aspect.html">r.slope.aspect</a>,
<a href="r.spread.html">r.spread</a>,
<a href="r.spreadpath.html">r.spreadpath</a>
</em>

Sample data download: <a href="https://grass.osgeo.org/download/data/">firedemo.sh</a>
(run this script within the "Fire simulation data set" location.

<h2> AUTHOR</h2>

Jianping Xu, Center for Remote Sensing and Spatial Analysis, Rutgers University.

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